In the integrated circuit (IC) industry, it is important to obtain atomically or near atomically clean substrate surfaces prior to formation of various films over the top of these surfaces. Specifically, various processing steps, such as the formation of silicide layers on semiconductive surfaces, the formation of glue layers between two layers of material on an IC, and the formation of inlaid barrier layers to protect dielectric layers from metallic contaminants within the inlaid interconnect are very sensitive to surface cleanliness. If a sufficiently clean surface is not properly formed before deposition of these types of surface-critical films, contact/via resistance may be too high, poor adhesion between layers of material may result wherein IC reliability is reduced, retarded film formation may occur (e.g., a silicide may never properly form), and/or poor texture and/or grain structure may result in the sputtered film.
In order to attempt to clean a surface of a substrate before film deposition to avoid the above disadvantages, current IC manufacturers use one chamber for substrate surface cleaning and a separate chamber for film sputtering. A wafer is first positioned within the cleaning chamber in order to initiate a cleaning operation of the wafer surface. The wafer is then moved from the cleaning chamber to a deposition chamber to form the required sputter film on the previously-cleaned substrate surface.
However, this two-chamber process is disadvantageous for several reasons. First, any time a wafer is transferred between chambers, even in a cluster tool, there is a tendency for the wafer surface to become contaminated with harmful contaminants such as heavy metals. There is also a tendency for the wafer surface to become oxidized by exposure to an oxidation ambient during the transfer. This oxidation or contamination of the surface can result in all of the disadvantages discussed above (e.g., poor interconnect conductivity, poor film adhesion, etc.). In addition, the maintenance and operation of two separate chambers is expensive and the throughput of wafers through a two-chamber system can be substantially reduced. The increased maintenance and reduced throughput will adversely increase IC manufacturing costs.
In addition to using a two-chamber approach, another known method uses reactive chemical cleans that are insitu with the deposition/sputter process in order to clean the substrate surface before film formation. Typically, the reactive chemistries that are used contain either chlorine (Cl) or fluorine (F). In this insitu chemical surface clean method, the surface that requires cleaning is exposed to Cl or F gas. The Cl or F gas is heated to initiate a chemical reaction with the wafer surface causing a chemical clean, that has no physical cleaning action, over the wafer surface.
A disadvantage with this non-physical chemical clean is that it typically requires higher temperatures in order to enable the required chemical reaction. Higher temperatures are typically disadvantageous in the IC industry since certain semiconductor films and doped junctions are adversely affected by higher temperatures. In addition, the use of reactive chemistries to perform surface cleans may leave residual Cl or F material on various exposed surfaces of the substrate. Residual F material can form undesired compounds (e.g. hydrofluoric acid, HF) which can etch or otherwise damage layers within the IC after their formation. In addition, the presence of residual Cl is disadvantageous since it is very corrosive to metals, and may also form damaging compounds within the IC after its formation and may react with the sputter material itself. Furthermore, the use of an insitu reactive chemistry to form a clean surface increases the cost of the processing chamber. Such a processing chamber must be made more robust to resist the corrosive properties of the reactive chemistries. In addition to necessitating a more expensive chamber, these reactive chemistry processes also increase chamber maintenance costs.
Therefore, a need exists in the industry for a method to form clean surfaces prior to sputtered film formation whereby one or more of reduced via or contact resistance, improved film adhesion, improved film formation, improved film grain structure, reduced process temperature, reduced wafer costs, improved wafer throughput, reduced chamber maintenance, and/or reduced presence of volatile IC residuals (e.g., reduced use of Cl and F) is obtained.